jdk11_headless fails to build

[ivan]

Issue description

The jdk11_headless build fails with:

checking user specified JVM feature list... 
configure: Unknown JVM features specified: "zgc--enable-headless-only"
configure: The available JVM features are: "aot cds cmsgc compiler1 compiler2 dtrace epsilongc g1gc graal jfr jni-check jvmci jvmti link-time-opt management minimal nmt parallelgc serialgc services static-build vm-structs zero zgc"
configure: error: Cannot continue
configure exiting with result code 1
builder for '/nix/store/8zw1qb4hp137iv01v9p5f11f0yq3d5vd-openjdk-11.0.1-b13.drv' failed with exit code 1

https://hydra.nixos.org/build/85397596

It was previously succeeding: Last successful build 2018-11-15 07:23:10 https://hydra.nixos.org/build/84076828

Steps to reproduce

Technical details

Please run nix-shell -p nix-info --run "nix-info -m" and paste the
results.

[ivan]

1629147 appears to be lacking some spaces between arguments, and I'll submit a PR.